More specifically, the invention relates to a hinge mechanism for a vehicle seat, comprising:                first and second frames mounted so that they can rotate relative to one another about an axis, said frames comprising inner faces oriented inward and facing one another, outer faces oriented outward and away from each other, and circular peripheral edges distanced from the axis, and        an annular ring comprising a base which covers the peripheral edges of the frames, and first and second side flaps which cover at least a portion of each of the outer faces.        
Document FR-A-2 915 436 describes an example of a hinge mechanism of this type, which has been satisfactory and in which the ring additionally comprises a shoulder pressing on the inner face of the second frame. This allows shaping the second flap by crimping it between the inner face and the outer face of the second frame. Due to this shoulder of the ring and this crimping process, the first frame is not held by the crimping of the first flap of the ring, which would prevent the first frame from rotating relative to the second frame. Operating clearances are maintained between the first frame and the ring, then between the second frame and the first frame, which allows the rotation to occur.
The goal of the invention is to propose an alternative assembly of the first and second frames which must be rotatable relative to each other.